Connectitut Emerging Infections Program, Yale School of Public Health, New Haven.

12

Ohio Department of Health, Columbus.

13

Michigan Department of Community Health, Lansing.

14

Minnesota Department of Health, St Paul.

15

Oregon Public Health Division, Portland.

16

Vanderbilt University School of Medicine, Nashville, Tennessee.

Abstract

Background:

We investigated the effect of influenza vaccination on disease severity in adults hospitalized with laboratory-confirmed influenza during 2013-14, a season in which vaccine viruses were antigenically similar to those circulating.

Methods:

We analyzed data from the 2013-14 influenza season and used propensity score matching to account for the probability of vaccination within age strata (18-49, 50-64, and ≥65 years). Death, intensive care unit (ICU) admission, and hospital and ICU lengths of stay (LOS) were outcome measures for severity. Multivariable logistic regression and competing risk models were used to compare disease severity between vaccinated and unvaccinated patients, adjusting for timing of antiviral treatment and time from illness onset to hospitalization.